Method of selectively etching first region made of silicon nitride against second region made of silicon oxide

ABSTRACT

Generation of a deposit can be suppressed and high selectivity can be acquired when etching a first region made of silicon nitride selectively against a second region made of silicon oxide. A method includes preparing a processing target object having the first region and the second region within a chamber provided in a chamber main body of a plasma processing apparatus; generating plasma of a first gas including a gas containing hydrogen within the chamber to form a modified region by modifying a part of the first region with active species of the hydrogen; and generating plasma of a second gas including a gas containing fluorine within the chamber to remove the modified region with active species of the fluorine.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Japanese Patent Application Nos.2016-240871 and 2017-086521 filed on Dec. 13, 2016 and Apr. 25, 2017,respectively, the entire disclosures of which are incorporated herein byreference.

TECHNICAL FIELD

The embodiments described herein pertain generally to a method ofetching a first region made of silicon nitride selectively against asecond region made of silicon oxide.

BACKGROUND

In the manufacture of an electronic device such as a semiconductordevice, it may be required to etch one of two regions made of differentmaterials selectively against the other. For example, it may be neededto etch a first region made of silicon nitride selectively against asecond region made of silicon oxide.

Generally, in order to etch the first region made of the silicon nitrideselectively against the second region made of the silicon oxide, plasmaetching using a hydrofluorocarbon gas is performed. In the plasmaetching using the hydrofluorocarbon gas, the first region is etched byactive species in plasma while the second region is protected by adeposit of fluorocarbon. This plasma etching is described in PatentDocument 1.

Patent Document 1: Japanese Patent Laid-open Publication No. 2003-229418

To etch the first region made of the silicon nitride selectively againstthe second region made of the silicon oxide, however, a selectivityhigher than a selectivity in the plasma etching using thehydrofluorocarbon gas is needed.

Furthermore, in the plasma etching using the hydrofluorocarbon gas, thesecond region is protected by using the deposit as stated above. If,however, a narrow opening is formed as the etching of the first regionprogresses, the opening may be clogged with the corresponding deposit,so that the etching of the first region is stopped.

In view of the foregoing, when etching the first region made of thesilicon nitride selectively against the second region made of thesilicon oxide, it is required to suppress generation of the deposit andacquire the high selectivity.

SUMMARY

In one exemplary embodiment, there is provided a method of etching afirst region made of silicon nitride selectively against a second regionmade of silicon oxide. The method includes (i) preparing a processingtarget object having the first region and the second region within achamber provided in a chamber main body of a plasma processingapparatus; (ii) generating plasma of a first gas including a gascontaining hydrogen within the chamber to form a modified region bymodifying a part of the first region with active species of the hydrogen(hereinafter, referred to as “modifying process”); and (iii) generatingplasma of a second gas including a gas containing fluorine within thechamber to remove the modified region with active species of thefluorine (hereinafter, referred to as “removing process”).

In the method, the part of the first region is modified by the activespecies of the hydrogen generated in the modifying process and becomesthe modified region which can be easily removed by the active species ofthe fluorine. Meanwhile, since the second region made of silicon oxideis stabilized, the second region is not modified by the active speciesof the hydrogen. Accordingly, in the removing process, the modifiedregion is removed selectively against the second region. Therefore,according to the method, the first region is selectively etched againstthe second region. Furthermore, the active species in the plasmagenerated in the modifying process and the removing process have a verylow deposition property as compared to active species of plasma of ahydrofluorocarbon gas, or has substantially no deposition property.Thus, according to the method, generation of a deposit is suppressed.

The processing target object may be placed, within the chamber, on astage including therein an electrode to which a high frequency power forattracting ions onto the processing target object, that is, a highfrequency bias power is allowed to be supplied. The high frequency biaspower may be supplied to the electrode in the modifying process.According to the exemplary embodiment, the modification of the firstregion is more efficiently performed. The high frequency bias power maynot be supplied to the electrode in the generating of the plasma of thesecond gas. According to the exemplary embodiment, the modified regionis removed by, not a sputter etching by ions, a chemical reactionbetween the modified region and the active species of the fluorine.

The second gas may include a NF₃ gas as the gas containing fluorine.

The second gas may further include hydrogen. A ratio of a number ofatoms of the hydrogen in the second gas to a number of atoms of thefluorine in the second gas is equal to or higher than 8/9. By the plasmaof the second gas, etching selectivity of the first region is furtherimproved.

The second gas may include a NF₃ gas as the gas containing fluorine, andmay further include a H₂ gas.

A flow rate ratio of the H₂ gas in the second gas to the NF₃ gas in thesecond gas may be equal to or higher than 3/4. By the plasma of thesecond gas, the etching selectivity of the first region is furtherimproved.

The first gas may include a H₂ gas as the gas containing hydrogen.

A plurality of sequences each of which includes the modifying processand the removing process may be performed in sequence.

The processing target object may further have a third region made ofsilicon. The first gas may further include a gas containing oxygen. Inthe modifying process of the present exemplary embodiment, a surface ofthe third region is oxidized by active species of oxygen in the firstgas, and etching of the third region is suppressed in the etching by theremoving process. Accordingly, the first region is etched selectivelyagainst the second region and the third region. The first region may beprovided to cover the second region and the third region.

A plurality of sequences each of which includes the modifying processand the removing process are performed in sequence. The processingtarget object further has a third region made of silicon. The firstregion is provided to cover the second region and the third regionbefore the plurality of sequences are performed. The plurality ofsequences include one or more first sequences and one or more secondsequences. Among the plurality of sequences, the one or more firstsequences are performed until a time immediately before the third regionis exposed or until the third region is exposed. Among the plurality ofsequences, the one or more second sequences are performed to oxidize asurface of the third region after the one or more first sequences. Thefirst gas further includes a gas containing oxygen in at least onesecond sequence. In the modifying process of the present exemplaryembodiment, the surface of the third region is oxidized and the etchingof the third region is suppressed in the etching by the removingprocess. Accordingly, the first region is etched selectively against thesecond region and the third region.

The first gas may not contain the gas containing oxygen in the one ormore first sequences. The plurality of sequences may further include oneor more third sequences. Among the plurality of sequences, the one ormore third sequences are performed after the one or more secondsequences. Only in the one or more third sequences, or in the one ormore third sequences in addition to the one or more first sequences, thefirst gas may not include the gas containing oxygen.

A flow rate ratio of the gas containing oxygen in the first gas to thegas containing hydrogen in the first gas may be set to be in a rangefrom 3/100 to 9/100. According to the present exemplary embodiment, thefirst region can be etched against the third region with a higherselectivity.

The gas containing oxygen may be an O₂ gas.

According to the exemplary embodiments, it is possible to suppress thegeneration of the deposit and achieve the high selectivity in etchingthe first region made of the silicon nitride selectively against thesecond region made of the silicon oxide.

The foregoing summary is illustrative only and is not intended to be inany way limiting. In addition to the illustrative aspects, embodiments,and features described above, further aspects, embodiments, and featureswill become apparent by reference to the drawings and the followingdetailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

In the detailed description that follows, embodiments are described asillustrations only since various changes and modifications will becomeapparent to those skilled in the art from the following detaileddescription. The use of the same reference numbers in different figuresindicates similar or identical items.

FIG. 1 is a flowchart for describing a method according to an exemplaryembodiment;

FIG. 2 is an enlarged cross sectional view illustrating a part of anexample processing target object to which the method according to theexemplary embodiment is applicable;

FIG. 3 is an enlarged cross sectional view illustrating a part ofanother example processing target object to which the method accordingto the exemplary embodiment is applicable;

FIG. 4 is a diagram schematically illustrating a plasma processingapparatus in which methods according to various exemplary embodimentsare performed;

FIG. 5A is a diagram for describing a process ST1 of the methodaccording to the exemplary embodiment and FIG. 5B is a diagramillustrating a state of the processing target object after the processST1 of the method according to the exemplary embodiment is performed;

FIG. 6A is a diagram for describing a process ST2 of the methodaccording to the exemplary embodiment, FIG. 6B is a diagram illustratinga state of the processing target object after the process ST2 of themethod according to the exemplary embodiment is performed, and FIG. 6Cis a diagram illustrating a state of the processing target object uponthe completion of the method according to the exemplary embodiment;

FIG. 7A is a diagram illustrating a state of the processing targetobject after the process ST1 of the method according to the exemplaryembodiment is performed, FIG. 7B is a diagram illustrating a state ofthe processing target object after the process ST2 of the methodaccording to the exemplary embodiment is performed, and FIG. 7C is adiagram illustrating a state of the processing target object upon thecompletion of the method according to the exemplary embodiment;

FIG. 8 is a flowchart for describing a method according to anotherexemplary embodiment;

FIG. 9A and FIG. 9B are diagrams for respectively describing a processST1 of a first sequence and a process ST1 of a second sequence in afirst example of the method shown in FIG. 8, and FIG. 9C is a diagramillustrating a state where a surface of a third region is oxidized as aresult of performing the process ST1 of the second sequence;

FIG. 10A and FIG. 1013 are diagrams for respectively describing aprocess ST1 of a first sequence and a process ST1 of a second sequencein a second example of the method shown in FIG. 8, and FIG. 10C is adiagram illustrating a state where the surface of the third region isoxidized as a result of performing the process ST1 of the secondsequence;

FIG. 11 is a flowchart for describing a method according to stillanother exemplary embodiment;

FIG. 12A to FIG. 12C are diagrams for respectively describing a processST1 of a first sequence, a process ST1 of a second sequence and aprocess ST1 of a third sequence in the method shown in FIG. 11;

FIG. 13A to FIG. 13C are graphs showing a result of a first experiment;

FIG. 14A and FIG. 14B are graphs showing a result of a secondexperiment;

FIG. 15 is a graph showing a result of the second experiment;

FIG. 16A is a diagram for describing a decrement obtained for eachsample in a third experiment and FIG. 16B is a table showing thedecrement obtained for each sample in the third experiment;

FIG. 17 is a flowchart for describing a method according to still yetanother exemplary embodiment;

FIG. 18 is an enlarged cross sectional view illustrating a part of aprocessing target object to which the method of FIG. 17 is applied;

FIG. 19 is a cross sectional view illustrating a state of the part ofthe processing target object in the middle of performing the method ofFIG. 17;

FIG. 20 is a cross sectional view illustrating a state of the part ofthe processing target object in the middle of performing the method ofFIG. 17;

FIG. 21 is a cross sectional view illustrating a state of the part ofthe processing target object in the middle of performing the method ofFIG. 17;

FIG. 22 is a cross sectional view illustrating a state of the part ofthe processing target object in the middle of performing the method ofFIG. 17;

FIG. 23 is a cross sectional view illustrating a state of the part ofthe processing target object after the method of FIG. 17 is performed;

FIG. 24 is a flowchart for describing a part of processes of the methodshown in FIG. 17 in detail; and

FIG. 25A and FIG. 25B are flowcharts each for describing a part of theprocesses of the method shown in FIG. 17 in detail.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part of the description. In thedrawings, similar symbols typically identify similar components, unlesscontext dictates otherwise. Furthermore, unless otherwise noted, thedescription of each successive drawing may reference features from oneor more of the previous drawings to provide clearer context and a moresubstantive explanation of the current exemplary embodiment. Still, theexemplary embodiments described in the detailed description, drawings,and claims are not meant to be limiting. Other embodiments may beutilized, and other changes may be made, without departing from thespirit or scope of the subject matter presented herein. It will bereadily understood that the aspects of the present disclosure, asgenerally described herein and illustrated in the drawings, may bearranged, substituted, combined, separated, and designed in a widevariety of different configurations, all of which are explicitlycontemplated herein

Hereinafter, various exemplary embodiments will be described in detailwith reference to the accompanying drawings. In the various drawings,same or corresponding parts will be assigned same reference numerals.

FIG. 1 is a flowchart for describing a method according to an exemplaryembodiment. A method MT shown in FIG. 1 is a method of etching a firstregion made of silicon nitride selectively against a second region madeof silicon oxide. According to the exemplary embodiment, in the methodMT, the first region is selectively etched against the second region anda third region made of silicon. In a process STP of the method MT, aprocessing target object is prepared within a chamber provided in achamber main body of a plasma processing apparatus.

FIG. 2 is an enlarged cross sectional view illustrating a part of anexample processing target object to which the method according to theexemplary embodiment is applicable. A processing target object W shownin FIG. 2 has a first region R1 and a second region R2. The processingtarget object W may further have a third region R3. The first region R1is made of silicon nitride; the second region R2, silicon oxide; and thethird region R3, silicon. The third region R3 is made of, by way ofexample, polycrystalline silicon. In the processing target object Wshown in FIG. 2, the first region R1, the second region R2 and the thirdregion R3 are provided on an underlying layer UL. A layout of the firstregion R1, the second region R2 and the third region R3 of theprocessing target object W is not limited to the example shown in FIG.2.

FIG. 3 is an enlarged cross sectional view illustrating a part ofanother example processing target object to which the method accordingto the exemplary embodiment is applicable. A processing target object Wshown in FIG. 3 has, like the processing target object W shown in FIG.2, a first region R1, a second region R2 and a third region R3. Thesecond region R2 is provided at both sides of the third region R3, andthe third region R3 is protruded above the second region R2. The firstregion R1 is provided to cover the second region R2 and the third regionR3. Further, the processing target object W shown in FIG. 3 is anintermediate product obtained in the course of manufacturing a fin typefield effect transistor. The third region R3 is used as a fin regionwhich provides a source region, a drain region and a channel region.

FIG. 4 is a diagram schematically illustrating a plasma processingapparatus in which methods according to various exemplary embodimentsare performed. A plasma processing apparatus 10 shown in FIG. 4 isequipped with an ICP (Inductively Coupled Plasma) type plasma source.The plasma processing apparatus 10 includes a chamber main body 12. Thechamber main body 12 is made of a metal such as, but not limited to,aluminum. The chamber main body 12 has, for example, a substantiallycylindrical shape. An internal space of the chamber main body 12 isprovided as a chamber 12 c. The chamber 12 c serves as a space for aplasma processing.

A stage 14 is provided at a bottom portion of the chamber main body 12.The stage 14 is configured to hold the processing target object Wmounted thereon. The stage 14 is supported by a supporting member 13. Inthe chamber 12 c, the supporting member 13 is extended upwards from thebottom portion of the chamber main body 12. The supporting member 13 mayhave, for example, a substantially cylindrical shape. The supportingmember 13 may be made of an insulating material such as, but not limitedto, quartz.

The stage 14 is equipped with an electrostatic chuck 16 and a lowerelectrode 18. The lower electrode 18 includes a first plate 18 a and asecond plate 18 b. The first plate 18 a and the second plate 18 b aremade of a metal such as, but not limited to, aluminum. The first plate18 a and the second plate 18 b may have, for example, a substantiallycircular plate shape. The second plate 18 b is provided on the firstplate 18 a. The second plate 18 b is electrically connected with thefirst plate 18 a.

The electrostatic chuck 16 is provided on the second plate 18 b. Theelectrostatic chuck 16 includes an insulating layer and a film-shapedelectrode embedded in the insulating layer. The electrode of theelectrostatic chuck 16 is electrically connected to a DC power supply 22via a switch 23. The electrostatic chuck 16 generates an electrostaticforce by a DC voltage applied from the DC power supply 22. Theprocessing target object W is attracted to and held by the electrostaticchuck 16 by the electrostatic force.

In the plasma processing apparatus 10, a focus ring FR is placed on aperipheral portion of the second plate 18 b to surround an edge of theprocessing target object W and an edge of the electrostatic chuck 16.The focus ring FR is configured to improve uniformity of a plasmaprocessing. The focus ring FR is made of, by way of example, but notlimitation, quartz.

The second plate 18 b is provided with a flow path 24. A heat exchangemedium, for example, a coolant is supplied into the flow path 24 from atemperature controller (e.g., a chiller unit) provided outside thechamber main body 12 to adjust a temperature of the stage 14. Thetemperature controller is a device configured to adjust a temperature ofthe heat exchange medium. The heat exchange medium is supplied into theflow path 24 from the temperature controller via a pipeline 26 a. Theheat exchange medium supplied into the flow path 24 is then returnedback to the temperature controller via a pipeline 26 b. As the heatexchange medium the temperature of which is adjusted by the temperaturecontroller is supplied into the flow path 24 of the stage 14, thetemperature of the stage 14 is adjusted and, ultimately, a temperatureof the processing target object W is adjusted. In the plasma processingapparatus 10, a gas supply line 28 is extended up to a top surface ofthe electrostatic chuck 16 through the stage 14. A heat transfer gassuch as, but not limited to, a He gas is supplied into a gap between thetop surface of the electrostatic chuck 16 and a rear surface of theprocessing target object W from a heat transfer gas supply devicethrough the gas supply line 28. Accordingly, a heat exchange between thestage 14 and the processing target object W is facilitated.

A heater HT may be provided within the stage 14. The heater HT is aheating element. For example, the heater HT is buried in the secondplate 18 b or the electrostatic chuck 16. The heater HT is connected toa heater power supply HP. As a power is supplied from the heater powersupply HP to the heater HT, the temperature of the stage 14 is adjustedand, ultimately, the temperature of the processing target object W isadjusted.

A high frequency power supply 30 is connected to the lower electrode 18of the stage 14 via a matching device 32. A high frequency power fromthe high frequency power supply 30 may be applied to the lower electrode18. The high frequency power supply 30 is configured to generate a highfrequency power for ion attraction into the processing target object Wmounted on the stage 14, i.e., a high frequency bias power. By way ofexample, the high frequency bias power has a frequency in a range from400 kHz to 40.68 MHz, for example, 13.56 MHz. The matching device 32 hasa circuit configured to match an output impedance of the high frequencypower supply 30 and an impedance at a load side (lower electrode 18).Further, in the plasma processing apparatus 10, it may be also possibleto generate plasma by applying the high frequency bias power to thelower electrode 18 without applying another high frequency power forplasma generation.

In the plasma processing apparatus 10, a shield 34 is provided along aninner wall of the chamber main body 12 in a detachable manner. Theshield 34 is also provided on an outer side surface of the supportingmember 13. The shield 34 is a member configured to suppress an etchingbyproduct from adhering to the chamber main body 12. The shield 34 maybe formed by coating a surface of an aluminum base member with ceramicsuch as Y₂O₃.

A gas exhaust path is formed between the stage 14 and a sidewall of thechamber main body 12. This gas exhaust path is connected to a gasexhaust port 12 e formed at the bottom portion of the chamber main body12. The gas exhaust port 12 e is connected to a gas exhaust device 38via a pipeline 36. The gas exhaust device 38 includes a pressurecontroller and a vacuum pump such as a turbo molecular pump. A baffleplate 40 is provided at the gas exhaust path, i.e., between the stage 14and the sidewall of the chamber main body 12. The baffle plate 40 isprovided with a multiple number of through holes in a thicknessdirection thereof. For example, the baffle plate 40 is formed by coatingan aluminum base member with ceramic such as Y₂O₃.

A ceiling portion of the chamber main body 12 is opened. This opening isclosed by a window member 42. The window member 42 is made of adielectric material such as quartz. The window member 42 has, forexample, a plate shape.

A gas inlet opening 12 i is formed at the sidewall of the chamber mainbody 12. The gas inlet opening 12 i is connected to a gas supply unit 44via a pipeline 46. The gas supply unit 44 is configured to supply afirst gas and a second gas to be described later into the chamber 12 c.The gas supply unit 44 is equipped with a gas source group 44 a, a flowrate controller group 44 b and a valve group 44 c. The gas source group44 a includes multiple gas sources. These gas sources include sources ofone or more gases contained in the first gas and sources of one or moregases contained in the second gas. The flow rate controller group 44 bincludes multiple flow rate controllers. Each of these flow ratecontrollers is implemented by a mass flow controller or a pressurecontrol type flow rate controller. The valve group 44 c includesmultiple valves. Each of the multiple gas sources of the gas sourcegroup 44 a is connected to the gas inlet opening 12 i via thecorresponding one of the multiple flow rate controllers of the flow ratecontroller group 44 b and the corresponding one of the multiple valvesof the valve group 44 c. Further, the gas inlet opening 12 i may beformed at a position other than the sidewall of the chamber main body12, for example, at the window member 42.

An opening 12 p is formed at the sidewall of the chamber main body 12.The opening 12 p is a passageway through which the processing targetobject W passes when the processing target object W is carried into thechamber 12 c from outside the chamber main body 12 or when theprocessing target object W is carried out of the chamber main body 12from the chamber 12 c. Further, a gate valve 48 configured to open/closethe opening 12 p is provided at the sidewall of the chamber main body12.

An antenna 50 and a shield member 60 are provided above the ceilingportion of the chamber main body 12 and the window member 42. Theantenna 50 and the shield member 60 are provided at an outside of thechamber main body 12. In the exemplary embodiment, the antenna 50includes an inner antenna element 52A and an outer antenna element 52B.The inner antenna element 52A is a spiral coil and is extended above acentral portion of the window member 42. The outer antenna element 52Bis a spiral coil and is extended above the window member 42 and outsidethe inner antenna element 52A. Each of the inner antenna element 52A andthe outer antenna element 52B is made of a conductor such as, but notlimited to, copper, aluminum or stainless steel.

The inner antenna element 52A and the outer antenna element 52B are heldand supported by a plurality of supporting body 54. For example, each ofthe supporting body 54 has a rod shape. These supporting body 54 areextended in a radial shape from a center of the inner antenna element52A to an outside of the outer antenna element 52B.

The shield member 60 encloses the antenna 50. The shield member 60 hasan inner shield wall 62A and an outer shield wall 62B. The inner shieldwall 62A has a cylindrical shape and is provided between the innerantenna element 52A and the outer antenna element 52B to surround theinner antenna element 52A. The outer shield wall 62B has a cylindricalshape and is provided at outside the outer antenna element 52B tosurround the outer antenna element 52B.

A disk-shaped inner shield plate 64A is placed above the inner antennaelement 52A to close an opening of the inner shield wall 62A. An annularplate-shaped outer shield plate 64B is placed above the outer antennaelement 52B to close an opening between the inner shield wall 62A andthe outer shield wall 62B.

The shapes of the shield walls and the shield plates of the shieldmember 60 may not be limited to the aforementioned examples. The shapeof the shield walls of the shield member 60 may be of another shape suchas a rectangular cylindrical shape.

A high frequency power supply 70A is connected to the inner antennaelement 52A, and a high frequency power supply 70B is connected to theouter antenna element 52B. High frequency powers having the same ordifferent frequencies are supplied to the inner antenna element 52A andthe outer antenna element 52B from the high frequency power supply 70Aand the high frequency power supply 70B, respectively. If the highfrequency power from the high frequency power supply 70A is supplied tothe inner antenna element 52A, an induction field is generated withinthe chamber 12 c, so that a gas within the chamber 12 c is excited bythe induction field. As a result, plasma is generated above a centralregion of the processing target object W. Further, if the high frequencypower is supplied from the high frequency power supply 70B to the outerantenna element 52B, an induction field is generated within the chamber12 c, so that the gas within the chamber 12 c is excited by thisinduction field. Accordingly, a ring-shaped plasma is generated above aperipheral region of the processing target object W.

Further, electrical lengths of the inner antenna element 52A and theouter antenna element 52B need to be adjusted depending on the highfrequency powers respectively output from the high frequency powersupplies 70A and 70B. For the purpose, positions of the inner shieldplate 64A and the outer shield plate 64B in a height direction areindividually adjusted by an actuator 68A and an actuator 68B,respectively.

The plasma processing apparatus 10 may further include a control unit80. The control unit 80 may be implemented by a computer including aprocessor, a storage unit such as a memory, an input device, a displaydevice, and so forth. The control unit 80 is operated based on controlprograms and recipe data stored in the storage unit to control variouscomponents of the plasma processing apparatus 10. To elaborate, thecontrol unit 80 controls various components of the plasma processingapparatus 10 such as the multiple flow rate controllers of the flow ratecontroller group 44 b, the multiple valves of the valve group 44 c, thegas exhaust device 38, the high frequency power supply 70A, the highfrequency power supply 70B, the high frequency power supply 30, thematching device 32, the heater power supply HP, and so forth.Furthermore, when performing methods according to various exemplaryembodiments, the control unit 80 may control the various components ofthe plasma processing apparatus 10 based on control programs and recipedata.

Now, referring back to FIG. 1, the method MT will be explained indetail. Further, in the following description, reference is made to FIG.5A, FIG. 5B, FIG. 6A, FIG. 6B, FIG. 6C, FIG. 7A, FIG. 7B and FIG. 7C.FIG. 5A is a diagram for describing a process ST1 of the methodaccording to the exemplary embodiment, and FIG. 5B is a diagramillustrating a state of a processing target object after the process ST1of the method according to the exemplary embodiment is performed. FIG.6A is a diagram for describing a process ST2 of the method according tothe exemplary embodiment; FIG. 6B is a diagram illustrating a state ofthe processing target object after the process ST2 of the methodaccording to the exemplary embodiment is performed; and FIG. 6C is adiagram illustrating a state of the processing target object after themethod according to the exemplary embodiment is completed. FIG. 7A is adiagram illustrating a state of the processing target object after theprocess ST1 of the method according to the exemplary embodiment isperformed; FIG. 7B is a diagram illustrating a state of the processingtarget object after the process ST2 of the method according to theexemplary embodiment is performed; and FIG. 7C is a diagram illustratinga state of the processing target object after the method according tothe exemplary embodiment is completed.

As depicted in FIG. 1, in the process STP of the method MT, theprocessing target object W shown in FIG. 2 or FIG. 3 is prepared withina chamber provided by a chamber main body of a plasma processingapparatus. The processing target object W is placed on a stage having alower electrode. In case of using the plasma processing apparatus 10,the processing target object W is placed on the stage 14 and held by theelectrostatic chuck 16.

In the method MT, the process ST1 and the process ST2 are performed insequence in the state that the processing target object W is placed onthe stage 14. In the process ST1, plasma PL1 of a first gas is generatedwithin the chamber. The first gas includes a hydrogen-containing gas (agas containing hydrogen). The hydrogen-containing gas may be, by way ofnon-limiting example, a H₂ gas and/or a NH₃ gas.

In the process ST1, active species of hydrogen, for example, hydrogenions are irradiated from the plasma PL1 to a surface of the processingtarget object W, as illustrated in FIG. 5A. In FIG. 5A, each circularfigure surrounding a letter “H” represents the active species of thehydrogen. If the actives species of the hydrogen are irradiated to thesurface of the processing target object W, a part of the first regionR1, that is, a part of the first region R1 including a surface thereofis modified and becomes a modified region MR1, as depicted in FIG. 5B.In case that the processing target object W is as shown in FIG. 3, themodified region MR1 is formed as shown in FIG. 7A. The modified regionMR1 is easily removable by active species of fluorine. Meanwhile, asecond region R2 is stabilized and is not modified by the active speciesof the hydrogen.

In the process ST1 according to the exemplary embodiment, the highfrequency bias power is supplied to the lower electrode of the stage. Inthe process ST1, the plasma may be generated only by the high frequencybias power. If the high frequency bias power is supplied to the lowerelectrode, the hydrogen ions are strongly attracted into the processingtarget object W, so that the modification of the first region R1 isaccelerated and a thickness of the modified region MR1 in a thicknessdirection of the first region R1 is increased. Further, a power level ofthe high frequency bias power supplied to the lower electrode in theprocess ST1 is set such that etching by sputtering does not take place.

In case that the processing target object W has the third region R3, thefirst gas may further include an oxygen-containing gas (a gas containingoxygen). By way of non-limiting example, the oxygen-containing gas maybe one of an O₂ gas, a CO gas, a CO₂ gas, a NO gas, a NO₂ gas, a N₂O gasand a SO₂ gas or a mixed gas containing two or more of these gases. Incase that the first gas includes the oxygen-containing gas, activespecies of oxygen, for example, oxygen ions are irradiated to thesurface of the processing target object W, as illustrated in FIG. 5A. InFIG. 5A, each circular figure surrounding a letter “O” represents theactive species of the oxygen. If the actives species of the oxygen areirradiated to the surface of the processing target object W, a part ofthe third region R3, that is, a part of the third region R3 including asurface thereof is oxidized and becomes an oxidized region MR3, asdepicted in FIG. 5B. Once the surface of the third region R3 isoxidized, etching of the third region R3 is suppressed in the processST2 to be described later.

In the exemplary embodiment, a flow rate ratio of the oxygen-containinggas in the first gas to the hydrogen-containing gas in the first gas mayrange from 3/100 to 9/100. By setting the flow rate ratio of theoxygen-containing gas in the first gas to the hydrogen-containing gas inthe first gas to be in this range, the etching of the third region R3including the oxidized region MR3 is further suppressed in the processST2 to be described later. Furthermore, a reduction of an etching rateof the first region R1 is also suppressed in the second process ST2.

In the plasma processing apparatus 10, the first gas including thehydrogen-containing gas is supplied into the chamber 12 c from the gassupply unit 44 in the process ST1. The first gas supplied into thechamber 12 c may further include the oxygen-containing gas. A flow rateof each of the one or more gases included in the first gas is controlledby the corresponding one of the flow rate controllers of the flow ratecontroller group 44 b. Furthermore, a pressure of the chamber 12 c isset to a preset pressure by the gas exhaust device 38. Besides, the highfrequency bias power may be supplied to the lower electrode 18 from thehigh frequency power supply 30. In the process ST1, though the highfrequency powers may also be respectively supplied to the inner antennaelement 52A and the outer antenna element 52B from the high frequencypower supply 70A and the high frequency power supply 70B to generate theplasma, the supply of these high frequency powers to the antennaelements 52A and 52B is just optional. That is, in the process ST1, theplasma may be generated just by supplying the high frequency bias powerto the lower electrode 18, without applying any additional highfrequency power.

In the subsequent process ST2, plasma PL2 of a second gas may begenerated within the chamber. The second gas includes afluorine-containing gas (a gas containing fluorine). Thefluorine-containing gas may be any of various gases containing fluorine.By way of non-limiting example, the fluorine-containing gas may be oneof a NF₃ gas, a SF₆ gas and a fluorocarbon gas (e.g., a CF₄ gas) or amixed gas containing one or more of these gases. In addition to thefluorine-containing gas, the second gas may further include other gasessuch as, but not limited to, an O₂ gas and a rare gas such as an Ar gas.

In the process ST2, as depicted in FIG. 6A, the active species of thefluorine are irradiated to the surface of the processing target object Wfrom the plasma PL2. In FIG. 6A, each circular figure surrounding aletter “F” represents the active species of the fluorine. If the activesspecies of the fluorine are irradiated to the surface of the processingtarget object W, the modified region MR1 is selectively etched andremoved by the active species of the fluorine, as depicted in FIG. 6B.Further, as for the processing target object W as shown in FIG. 3, themodified region MR1 is removed, as depicted in FIG. 7B.

In the process ST2 according to the exemplary embodiment, the highfrequency bias power is not supplied to the lower electrode of thestage. If the high frequency bias power is not supplied to the lowerelectrode in the process ST2, the etching is performed mainly byfluorine radicals, not fluorine ions, as the active species of thefluorine. That is, not a sputter etching by ions but an etching by theradicals progresses. Accordingly, the etching of the second region R2and the third region R3 including the oxidized region MR3 is suppressed.Further, the modified region MR1 is removed by a chemical reactionbetween the modified region MR1 and the active species of the fluorine.

In the process ST2 according to the exemplary embodiment, the second gasmay further contain hydrogen. In case that the second gas contains thehydrogen, a ratio of a number of hydrogen atoms in the second gas to anumber of fluorine atoms in the second gas is set to be equal to orhigher than 8/9. Further, in case that the fluorine-containing gas is aNF₃ gas and the hydrogen-containing gas is a H₂ gas in the second gas, aflow rate ratio of the H₂ gas in the second gas to the NF₃ gas in thesecond gas is equal to or higher than 3/4. If the ratio of the number ofthe hydrogen atoms in the second gas to the number of the fluorine atomsin the second gas or the flow rate ratio of the H₂ gas in the second gasto the NF₃ gas in the second gas is set as stated above, siliconnitride, oxygen nitride and silicon are hardly etched. Silicon nitridemodified by hydrogen, however, is etched. That is, the modified regionMR1 is etched. Thus, etching selectivity for the first region R1 isfurther improved.

In the plasma processing apparatus 10, in the process ST2, the secondgas including the fluorine-containing gas is supplied into the chamber12 c from the gas supply unit 44. The second gas supplied into thechamber 12 c may further include the hydrogen-containing gas. A flowrate of each of the one or more gases included in the second gas iscontrolled by the corresponding one of the flow rate controllers of theflow rate controller group 44 b. Further, the pressure of the chamber 12c is set to a preset pressure by the gas exhaust device 38. Besides, thehigh frequency power is supplied to the inner antenna element 52A fromthe high frequency power supply 70A, and the high frequency power issupplied to the outer antenna element 52B from the high frequency powersupply 70B. The high frequency bias power from the high frequency powersupply 30 may not be supplied to the lower electrode 18 or, if supplied,the power level thereof is relatively low.

As shown in FIG. 1, in a subsequent process STJ, it is determinedwhether a stop condition is satisfied. It is determined that the stopcondition is satisfied when a repetition number of a sequence includingthe process ST1 and the process ST2 reaches a preset number. In theprocess STJ, if it is determined that the stop condition is notsatisfied, the process ST1 is performed again. Meanwhile, if it isdetermined that the stop condition is satisfied, the method MT is ended.By the time the method MT is completed, the first region R1 is removedfrom the processing target object W shown in FIG. 2, as can be seen fromFIG. 6C. Alternatively, the first region R1 is removed from theprocessing target object W shown in FIG. 3, as depicted in FIG. 7C.

In the method MT, the part of the first region R1 is modified by theactive species of the hydrogen generated in the process ST1 and becomesthe modified region MR1 which can be easily removed by the activespecies of the fluorine. Meanwhile, since the second region R2 made ofsilicon oxide is stabilized, the second region R2 is not modified by theactive species of the hydrogen. Accordingly, in the process ST2, themodified region MR1 is removed selectively against the second region R2.Therefore, according to the method MT, the first region R1 isselectively etched against the second region R2. Furthermore, the activespecies in the plasma generated in the process ST1 and the process ST2have a very low deposition property as compared to active species ofplasma of a hydrofluorocarbon gas, or has substantially no depositionproperty. Thus, according to the method MT, generation of a deposit issuppressed.

Moreover, if the processing target object W has the third region R3, thefirst gas includes the oxygen-containing gas as stated above.Accordingly, the surface of the third region R3 is oxidized by theactive species of the oxygen in the process ST1, and the etching of thethird region R3 including the oxidized region MR3 is suppressed in theetching of the process ST2. Accordingly, the first region R1 isselectively etched against the second region R2 and the third region R3.

Furthermore, in the exemplary embodiment as described above, the flowrate ratio of the oxygen-containing gas in the first gas to thehydrogen-containing gas in the first gas is set to be in a range from3/100 to 9/100. In the exemplary embodiment, the etching of the thirdregion R3 including the oxidized region MR3 is further suppressed in theprocess ST2. Further, the reduction of the etching rate of the firstregion R1 in the process ST2 is suppressed. As a consequence, the firstregion R1 can be selectively etched against the third region R3 with ahigher selectivity

Now, a method according to another exemplary embodiment will beexplained. FIG. 8 is a flowchart for describing the method according tothis exemplary embodiment. A method MTA shown in FIG. 8 is applicable toa processing target object in which a second region R2 and a thirdregion R3 are covered with a first region R1, like the processing targetobject W as shown in FIG. 3.

The method MTA includes a process STP which is the same as the processSTP of the method MT. The method MTA further includes multiple sequencesSQ which are performed in order. Each of the multiple sequences SQincludes a process ST1 which is the same as the process ST1 of themethod MT and a process ST2 which is the same as the process ST2 of themethod MT.

The multiple sequences SQ include one or more first sequences SQ1 andone or more second sequences SQ2. The one or more first sequences SQ1are one or more sequences including a sequence which is performed firstamong the multiple sequences. The one or more second sequences SQ2 aresequences performed after the one or more first sequences SQ1 among themultiple sequences SQ. The one or more second sequences SQ2 include aprocess ST1 for oxidizing the surface of the third region R3.

The method MTA includes a process STJ1 and a process STJ2. In theprocess STJ1, it is determined whether a stop condition is satisfied. Inthe process STJ1, it is determined that the stop condition is satisfiedwhen a repetition number of the first sequence SQ1 reaches a presetnumber. If it is determined in the process STJ1 that the stop conditionis not satisfied, the first sequence SQ1 is performed again. Meanwhile,if it is determined in the process STJ1 that the stop condition issatisfied, the processing progresses to the second sequence SQ2.

In the process STJ2, it is determined whether a stop condition issatisfied. In the process STJ2, it is determined that the stop conditionis satisfied when a repetition number of the second sequence SQ2 reachesa preset number. If it is determined in the process STJ2 that the stopcondition is not satisfied, the second sequence SQ2 is performed again.Meanwhile, if it is determined in the process STJ2 that the stopcondition is satisfied, the method MTA is ended.

FIG. 9A and FIG. 9B are diagrams for describing the process ST1 of thefirst sequence and the process ST1 of the second sequence in a firstexample of the method shown in FIG. 8. FIG. 9C is a diagram illustratinga state in which the surface of the third region is oxidized by theprocess ST1 of the second sequence. In the first example of the methodMTA, the one or more first sequences SQ1 are performed until the thirdregion R3 is exposed. In the first example of the method MTA, a firstgas used in the process ST1 of the one or more first sequences SQ1 doesnot include an oxygen-containing gas. Accordingly, as depicted in FIG.9A, in the process ST1 of the one or more first sequences SQ1, activespecies of oxygen are not irradiated to a processing target object W,and active species of hydrogen are irradiated to the processing targetobject W.

In the first example of the method MTA, the one or more second sequencesSQ2 are performed immediately after the third region R3 is exposed. Inthe process ST1 of the one or more second sequences SQ2, a first gasincludes an oxygen-containing gas in addition to a hydrogen-containinggas. Accordingly, in the first example of the method MTA, the activespecies of the hydrogen and the active species of the oxygen areirradiated to the processing target object W in the process ST1immediately after the third region R3 is exposed, as shown in FIG. 9B.Consequently, as depicted in FIG. 9C, immediately after the surface ofthe third region R3 is exposed, the surface of the third region R3 isoxidized, and an oxidized region MR3 is formed. Thus, the third regionR3 is protected from being etched by active species of fluorine in theprocess ST2. According to the first example of this method MTA, thefirst region R1 is selectively etched against the second region R2 andthe third region R3.

FIG. 10A and FIG. 10B are diagrams for describing the process ST1 of thefirst sequence and the process ST1 of the second sequence in a secondexample of the method shown in FIG. 8. FIG. 10C is a diagramillustrating a state in which the surface of the third region isoxidized by the process ST1 of the second sequence. In the secondexample of the method MTA, the one or more first sequences SQ1 areperformed until a time immediately before the third region R3 isexposed. That is, the one or more first sequences SQ1 are performeduntil there is created a state in which the first region R1 is slightlyleft to cover the third region R3. In the second example of the methodMTA, a first gas used in the process ST1 of the one or more firstsequences SQ1 does not include an oxygen-containing gas. Accordingly, asdepicted in FIG. 10A, in the process ST1 of the one or more firstsequences SQ1, active species of oxygen are not irradiated to aprocessing target object W, and active species of hydrogen areirradiated to the processing target object W.

In the one or more second sequences SQ2 of the second example of themethod MTA, a first gas includes an oxygen-containing gas in addition toa hydrogen-containing gas. Accordingly, in the second example of themethod MTA, the active species of the oxygen are irradiated to theprocessing target object W after the time immediately before the thirdregion R3 is exposed, as shown in FIG. 10B. Accordingly, as depicted inFIG. 10C, the surface of the third region R3 is oxidized immediatelyafter the surface of the third region R3 is exposed. Thus, after a timeimmediately after the surface of the third region R3 is exposed, thethird region R3 is protected from being etched by active species offluorine in the process ST2. According to the second example of thismethod MTA, the first region R1 is selectively etched against the secondregion R2 and the third region R3.

Now, a method according to still another exemplary embodiment will bediscussed. FIG. 11 is a flowchart for describing the method according tothis exemplary embodiment. A method MTB shown in FIG. 11 is applicableto a processing target object in which a second region R2 and a thirdregion R3 are covered with a first region R1, like the processing targetobject W as shown in FIG. 3, like the method MTA. The method MTB furtherincludes one or more third sequences SQ3 and a process STJ3 in additionto a process STP, one or more first sequences SQ1, a process STJ1, oneor more second sequences SQ2 and a process STJ2.

In the method MTB, the one or more second sequences SQ2 are ended aftera surface of the third region R3 is oxidized. In the method MTB, if itis determined in the process STJ2 that a stop condition is satisfied,the processing progresses to the third sequence SQ3. In the processSTJ3, it is determined whether a stop condition is satisfied. It isdetermined that the stop condition is satisfied when a repetition numberof the third sequence SQ3 reaches a preset number. If it is determinedin the process STJ3 that the stop condition is not satisfied, the thirdsequence SQ3 is performed again. Meanwhile, if it is determined in theprocess STJ3 that the stop condition is satisfied, the method MTB isended.

FIG. 12A, FIG. 12B and FIG. 12C are diagrams for describing a processST1 of the first sequence, a process ST1 of the second sequence and aprocess ST1 of the third sequence in the method shown in FIG. 11,respectively. In the method MTB, the one or more first sequences SQ1 areperformed until a time immediately before the third region R3 is exposedor until the third region R3 is exposed. In the process ST1 of the oneor more first sequences SQ1, a first gas does not include anoxygen-containing gas. Accordingly, as shown in FIG. 12A, in the processST1 of the one or more first sequences SQ1, active species of oxygen arenot irradiated to the processing target object W, and active species ofhydrogen are irradiated to the processing target object W. Further, inthe process ST1 of the one or more first sequences SQ1, the first gasmay include an oxygen-containing gas.

In the method MTB, the one or more second sequences SQ2 are performed tooxidize a surface of the third region R3 after the one or more firstsequences SQ1. In the process ST1 of the one or more second sequencesSQ2, a first gas has an oxygen-containing gas in addition to ahydrogen-containing gas. Thus, according to the one or more secondsequences SQ2 of the method MTB, active species of oxygen are irradiatedto the processing target object W immediately after the third region R3is exposed, as depicted in FIG. 12B. In the method MTB, the one or moresecond sequences SQ2 are ended after the surface of the third region R3is oxidized.

In the method MTB, the one or more third sequences SQ3 are performedafter the one or more second sequences SQ2. In the process ST1 of theone or more third sequences SQ3, a first gas does not include anoxygen-containing gas. Accordingly, as shown in FIG. 12C, in the processST1 of the one or more third sequences SQ3, active species of oxygen arenot irradiated to the processing target object W and active species ofhydrogen are irradiated to the processing target object W. In the methodMTB, since the surface of the third region R3 is oxidized immediatelyafter the third region R3 is exposed in the one or more second sequencesSQ2, the third region R3 is protected from being etched by activespecies of fluorine in a process ST2 even if the first gas does notinclude an oxygen-containing gas in the process ST1 of the one or morethird sequences SQ3. According to this method MTB, the first region R1is selectively etched against the second region R2 and the third regionR3.

Now, results of various experiments will be explained. However, thepresent disclosure is not limited thereto.

(First Experiment)

A first experiment is conducted to find a condition under which thesilicon nitride is not etched by the active species from the plasma ofthe second gas when the silicon nitride is not modified by the activespecies of the hydrogen. In the first experiment, a silicon nitridefilm, a silicon oxide film and a silicon film are processed by theplasma of the second gas within the chamber of the plasma processingapparatus 10. The second gas used in the first experiment contains a NF₃gas, a H₂ gas, an O₂ gas and an Ar gas. In the first experiment, theflow rate of the H₂ gas in the second gas is set to various values.Below, other parameters in the first experiment are specified.

<Parameters of the First Experiment>

-   -   Pressure of chamber 12 c: 400 mTorr (53.33 Pa)    -   High frequency power of high frequency power supplies 70A and        70B: 27 MHz, 600 W    -   High frequency bias power: 0 W    -   Flow rate of NF₃ gas: 45 sccm    -   Flow rate of O₂ gas: 300 sccm    -   Flow rate of Ar gas: 100 sccm    -   Processing time: 10 sec

In the first experiment, film thickness decrements (lengths), that is,etching amounts of the silicon nitride film, the silicon oxide film andthe silicon film by the processing with the plasma of the second gas arerespectively measured. FIG. 13A, FIG. 13B and FIG. 13C are graphsshowing results of the first experiment. In each of the graphs of FIG.13A to FIG. 13C, a horizontal axis represents a flow rate of the H₂ gasin the second gas. A vertical axis of the graph in FIG. 13A indicatesthe etching amount of the silicon nitride film; a vertical axis of thegraph in FIG. 13B, the etching amount of the silicon oxide film; and avertical axis of the graph in FIG. 13C, the etching amount of thesilicon film.

As can be seen from FIG. 13A, FIG. 13B and FIG. 13C, if the flow rate ofthe H₂ gas in the second gas is equal to or higher than 60 sccm, thesilicon nitride film, the silicon oxide film and the silicon film aresubstantially hardly etched in the processing with the plasma of thesecond gas. Accordingly, it is found out that the silicon nitride, thesilicon oxide and the silicon are not etched in the processing with theplasma of the second gas in which the flow rate ratio of the H₂ gas inthe second gas to the NF₃ gas in the second gas is equal to or higherthan 3/4. From this point of fact, it is confirmed that if the ratio ofthe number of hydrogen atoms in the second gas to the number of fluorineatoms in the second gas is equal to or higher than 8/9, the siliconnitride, the silicon oxide and the silicon are not etched in theprocessing with the plasma of the second gas.

(Second Experiment)

In a second experiment, the method MT is applied to a silicon nitridefilm, a silicon oxide film and a silicon film by using the plasmaprocessing apparatus 10, and a relationship between a flow rate ratio ofthe O₂ gas in the first gas to the H₂ gas in the first gas and anetching selectivity of the silicon nitride film against the siliconoxide film and the silicon film is obtained. In the second experiment, asequence including the process ST1 and the process ST2 is repeated 6times. Other parameters of the second experiment are as follows.

<Parameters of the Process ST1 in the Second Experiment>

-   -   Pressure of chamber 12 c: 30 mTorr (4 Pa)    -   High frequency power of high frequency power supplies 70A and        70B: 0 W    -   High frequency bias power: 13.56 MHz, 50 W    -   Flow rate of H₂ gas: 100 sccm    -   Processing time: 15 sec

<Parameters of the Process ST2 in the Second Experiment>

-   -   Pressure of chamber 12 c: 400 mTorr (53.33 Pa)    -   High frequency power of high frequency power supplies 70A and        70B: 27 MHz, 600 W    -   High frequency bias power: 0 W    -   Flow rate of NF₃ gas: 45 sccm    -   Flow rate of H₂ gas: 60 sccm    -   Flow rate of O₂ gas: 300 sccm    -   Flow rate of Ar gas: 100 sccm    -   Processing time: 10 sec

In the second experiment, film thickness decrements (lengths), that is,etching amounts of the silicon nitride film, the silicon oxide film andthe silicon film are respectively measured. Further, the ratio of theetching amount of the silicon nitride film to the etching amount of thesilicon film, that is, the etching selectivity of the silicon nitridefilm against the silicon film is calculated based on the etching amountsof the silicon nitride film and the silicon film. FIG. 14A, FIG. 14B andFIG. 15 show results thereof. In each of graphs in FIG. 14A, FIG. 14Band FIG. 15, a horizontal axis represents a flow rate ratio of the O₂gas to the H₂ gas. A vertical axis of the graph in FIG. 14A indicatesthe etching amount of the silicon nitride film; a vertical axis of thegraph in FIG. 14B, the etching amount of the silicon oxide film and theetching amount of the silicon film; and a vertical axis of the graph inFIG. 15, the etching selectivity of the silicon nitride film against thesilicon film.

As can be seen from FIG. 14B, if the flow rate ratio of the O₂ gas inthe first gas to the H₂ gas in the first gas is equal to or higher than3/100 (i.e., a percentage of 3%), the etching amount of the silicon filmis found to be decreased, that is, the etching of the silicon film isfound to be suppressed. Further, as can be seen from FIG. 14A, if theflow rate ratio of the O₂ gas in the first gas to the H₂ gas in thefirst gas is equal to or less than 9/100 (i.e., a percentage of 9%), theetching amount of the silicon nitride film is found to be almost equalto the etching amount of the silicon nitride film obtained when the flowrate ratio of the O₂ gas in the first gas to the H₂ gas in the first gasis zero (0). That is, in case that the flow rate ratio of the O₂ gas inthe first gas to the H₂ gas in the first gas is equal to or less than9/100, the etching amount of the silicon nitride film does notsubstantially decline. Accordingly, as shown in FIG. 15, it is found outthat the high etching selectivity of the silicon nitride film againstthe silicon film can be obtained if the flow rate ratio of the O₂ gas inthe first gas to the H₂ gas in the first gas is set to be in a rangefrom 3/100 to 9/100.

(Third Experiment)

In a third experiment, the method MT is applied to an experiment sample1 and an experiment sample 2, which are the same as the processingtarget object W shown in FIG. 3, by using the plasma processingapparatus 10. In the method MT applied to the experiment sample 1, thefirst gas does not contain an O₂ gas. Meanwhile, in the method MTapplied to the experiment sample 2, the first gas contains an O₂ gas.Further, a plasma processing using a processing gas containing ahydrofluorocarbon gas is performed on a comparative sample, which is thesame as the processing target object W shown in FIG. 3, by using theplasma processing apparatus 10. Below, parameters of the method MTapplied to the experiment sample 1, parameters of the method MT appliedto the experiment sample 2 and parameters of the plasma processingapplied to the comparative sample are specified. In addition, in themethod MT applied to the experiment sample 1 and the method MT appliedto the experiment sample 2, the processing is performed until the firstregion R1 is completed removed, and the sequence including the processST1 and the process ST2 is repeated thirty three (33) times. Likewise,in the plasma processing upon the comparative example, the processing isconducted until the first region R1 is completed removed.

<Parameters of the Process ST1 in the Method MT for the ExperimentSample 1 in the Third Experiment>

-   -   Pressure of chamber 12 c: 30 mTorr (4 Pa)    -   High frequency power of high frequency power supplies 70A and        70B: 0 W    -   High frequency bias power: 13.56 MHz, 50 W    -   Flow rate of H₂ gas: 100 sccm    -   Flow rate of O₂ gas: 0 sccm    -   Processing time: 15 sec

<Parameters of the Process ST2 in the Method MT for the ExperimentSample 1 in the Third Experiment>

-   -   Pressure of chamber 12 c: 400 mTorr (53.33 Pa)    -   High frequency power of high frequency power supplies 70A and        70B: 27 MHz, 600 W    -   High frequency bias power: 0 W    -   Flow rate of NF₃ gas: 45 sccm    -   Flow rate of H₂ gas: 60 sccm    -   Flow rate of O₂ gas: 300 sccm    -   Flow rate of Ar gas: 100 sccm    -   Processing time: 10 sec

<Parameters of the Process ST1 in the Method MT for the ExperimentSample 2 in the Third Experiment>

-   -   Pressure of chamber 12 c: 30 mTorr (4 Pa)    -   High frequency power of high frequency power supplies 70A and        70B: 0 W    -   High frequency bias power: 13.56 MHz, 50 W    -   Flow rate of H₂ gas: 100 sccm    -   Flow rate of O₂ gas: 9 sccm    -   Processing time: 15 sec

<Parameters of the Process ST2 in the Method MT for the ExperimentSample 2 in the Third Experiment>

-   -   Pressure of chamber 12 c: 400 mTorr (53.33 Pa)    -   High frequency power of high frequency power supplies 70A and        70B: 27 MHz, 600 W    -   High frequency bias power: 0 W    -   Flow rate of NF₃ gas: 45 sccm    -   Flow rate of H₂ gas: 60 sccm

Flow rate of O₂ gas: 300 sccm

-   -   Flow rate of Ar gas: 100 sccm    -   Processing time: 10 sec

<Parameters of the Plasma Processing Upon the Comparative Sample>

-   -   Pressure of chamber 12 c: 50 mTorr (6.666 Pa)    -   High frequency power of high frequency power supplies 70A and        70B: 27 MHz, 200 W    -   High frequency bias power: 50 W    -   Flow rate of CH₃F gas: 30 sccm    -   Flow rate of O₂ gas: 15 sccm    -   Flow rate of He gas: 500 sccm

FIG. 16A is a diagram for describing a decrement measured for each ofthe samples in the third experiment. In FIG. 16A, the second region R2and the third region R3 of each sample before the processing areindicated by dashed double-dotted lines, and the second region R2 andthe third region R3 of each sample after the processing are indicated bysolid lines. In the third experiment, as shown in FIG. 16A, a decrementΔL2 of the second region R2 and a decrement ΔL3 of the third region R3are obtained for each sample. Results are shown in a table of FIG. 16B.As can be seen from a result of the comparative sample shown in thetable of FIG. 16B, not only the first region R1 but also the secondregion R2 and the third region R3 are etched in the plasma processingwith the processing gas containing the hydrofluorocarbon gas. Meanwhile,as can be seen from a result of the experiment sample 1 shown in thetable of FIG. 16B, in the method MT, it is found out that the firstregion R1 can be etched selectively without etching the second region R2through the modification with the plasma of the first gas including thehydrogen-containing gas. In the method MT applied to the experimentsample 1, however, since the first gas does not include theoxygen-containing gas, the third region R3 is etched. In case of theexperiment sample 2 to which the method MT with the first gas includingthe oxygen-containing gas, it is found out that the first region R1 canbe etched selectively while etching neither the second region R2 nor thethird region R3.

Now, a method according to still yet another exemplary embodiment willbe discussed. FIG. 17 is a flowchart for describing the method accordingto this exemplary embodiment. In the following description, reference ismade to FIG. 18 to FIG. 25B together with FIG. 17. In a method MTC shownin FIG. 17, a sequence including the process ST1 and the process ST2 asstated above is performed one or more times after a second region isformed on a processing target object having a first region. Hereinafter,though the description is provided for the method MTC performed by usingthe plasma processing apparatus 10, the method MTC can be performed byusing a plasma processing apparatus other than the plasma processingapparatus 10.

In a process STP of the method MTC, a processing target object W shownin FIG. 18 is placed on the stage 14 of the plasma processing apparatus10. The processing target object W shown in FIG. 18 has an underlyinglayer UL and a region EL. The region EL is provided on the underlyinglayer UL. A surface of the underlying layer UL includes a main surfaceUL1. The main surface UL1 is perpendicular to a direction DR. Thedirection DR corresponds to the vertical direction in a state that theprocessing target object W is placed on the stage 14 (on theelectrostatic chuck 16).

The region EL has a plurality of protruded regions (e.g., a protrudedregion PJ1, a protruded region PJ2, etc.). Each of the plurality ofprotruded regions of the region EL is extended upwards from the mainsurface UL1. Each of the plurality of protruded regions of the region ELhas an end surface. The protruded region PJ1 has an end surface TE1. Theprotruded region PJ2 has an end surface TE2. On the processing targetobject W shown in FIG. 18, the end surface of each of the plurality ofprotruded regions of the region EL is exposed. That is, the end surfaceTE1 of the protruded region PJ1 is exposed, and the end surface TE2 ofthe protruded region PJ2 is exposed.

A height of each of the plurality of protruded regions is equivalent toa distance between the end surface thereof and the main surface UL1. Aheight TT1 of the protruded region PJ1 is a distance between the endsurface TE1 and the main surface UL1. A height TT2 of the protrudedregion PJ2 is a distance between the end surface TE2 and the mainsurface UL1. The heights of the plurality of protruded regions of theregion EL are different from each other. The protruded region PJ1 islower than the protruded region PJ2. That is, a value of the height TT1of the protruded region PJ1 is smaller than a value of the height TT2 ofthe protruded region PJ2.

The underlying layer UL is made of, by way of non-limiting example, Si(silicon). The region EL is made of, by way of example, but notlimitation, silicon nitride. That is, the entire region EL may be thefirst region made of silicon nitride. Alternatively, the plurality ofprotruded regions may be made of different materials. For example, apart of the plurality of protruded regions may be made of a materialdifferent from a material of the other protruded regions. By way ofnon-limiting example, the protruded region PJ1 may be made of siliconnitride, whereas the other region(s) may be made of one or more othermaterials such as silicon. In such a case, the protruded region PJ1 isthe first region made of silicon nitride.

End portions (portions including the end surface TE1, the end surfaceTE2, etc.) of the plurality of protruded regions (the protruded regionPJ1, the protruded region PJ2, etc.) of the region EL may be formed suchthat widths thereof are narrowed depending on a distance from the mainsurface UL1. That is, the end portions of the plurality of protrudedregions of the region EL may have a tapered shape. In case that the endportions of the plurality of protruded regions of the region EL have thetapered shape, widths of openings confined by the end portions of theplurality of protruded regions are relatively large. Thus, the formationof the deposit at the end portions of the protruded regions can besufficiently suppressed.

As depicted in FIG. 17, the process STP includes a process ST11 and aprocess ST12. In the process ST11, in the state that the processingtarget object W shown in FIG. 18 is placed on the stage 14, a first filmSF1 is conformally formed on a surface of the processing target objectW. The first film SF1 is made of silicon oxide. A film forming method ofthe process ST11 is an ALD (Atomic Layer Deposition) method. FIG. 24 isa detailed flowchart of the process ST11. As shown in FIG. 24, theprocess ST11 includes a process ST11 a, a process ST11 b, a process ST11c and a process ST11 d. The process ST11 a, the process ST11 b, theprocess ST11 c and the process ST11 d constitute a sequence SQ11. In theprocess ST11, the sequence SQ11 is performed one or more times.

In the process ST11 a, a third gas is supplied from the gas supply unit44 into the chamber 12 c in which the processing target object W isaccommodated. The third gas includes aminosilane-based gas, by way ofnon-limiting example, an organic-containing aminosilane-based gas. Byway of example, monoaminosilane (H₃—Si—R (R denotes anorganic-containing amino group)) may be used as the organic-containingaminosilane-based gas. In the process ST11 a, plasma of the third gas isnot generated. In the process ST11 a, molecules (e.g., monoaminosilane)in the third gas adhere to a surface of the processing target object Was a precursor. Further, the aminosilane-based gas included in the thirdgas may contain, besides the monoaminosilane, aminosilane having one tothree silicon atoms. Furthermore, the aminosilane-based gas included inthe third gas may contain aminosilane having one to three amino groups.

In the subsequent process ST11 b, the chamber 12 c is purged. That is,in the process ST11 b, the third gas is exhausted. In the process ST11b, an inert gas such as a nitrogen gas or a rare gas may be suppliedinto the chamber 12 c as a purge gas. In the process ST11 b, moleculesexcessively adhering on the processing target object W may be removed.By performing the process ST11 b, a layer of the precursor on theprocessing target object W becomes a very thin layer (e.g., amonomolecular layer).

In the process ST11 c, plasma of a fourth gas is generated within thechamber 12 c. The fourth gas includes a gas containing oxygen atoms. Thefourth gas may include, for example, an oxygen gas. In the process ST11c, the fourth gas is supplied into the chamber 12 c from the gas supplyunit 44. Further, the pressure of the chamber 12 c is set to apredetermined pressure by the gas exhaust device 38. Further, the highfrequency powers are respectively supplied to the inner antenna element52A and the outer antenna element 52B from the high frequency powersupply 70A and the high frequency power supply 70B. Further, the highfrequency bias power may be supplied to the lower electrode 18 from thehigh frequency power supply 30. In the process ST11 c, the fourth gas isexcited into the plasma. The layer of the precursor is exposed to activespecies of the oxygen from the plasma. As a result, the layer of theprecursor becomes a silicon oxide film (the first film SF1 or a partthereof).

In the subsequent process ST11 d, the chamber 12 c is purged. That is,in the process ST11 d, the fourth gas is exhausted. In the process ST11d, an inert gas such as a nitrogen gas or a rare gas may be suppliedinto the chamber 12 c as a purge gas.

In a subsequent process ST11 e, it is determined whether the sequenceSQ11 is to be ended. To elaborate, in the process ST11 e, it isdetermined whether a repetition number of the sequence SQ11 has reacheda preset number. If it is determined in the process ST11 e that therepetition number of the sequence SQ11 has not reach the preset number,the sequence SQ11 is performed again. Meanwhile, if it is determined inthe process ST11 e that the repetition number of the sequence SQ11 hasreached the preset number, the process ST11 is ended. As a result ofperforming the process ST11, the first film SF1 is conformally formed onthe surface of the processing target object W, as illustrated in FIG.19. A thickness of the first film SF1 is defined by the repetitionnumber of the sequence SQ11. That is, the thickness of the first filmSF1 is expressed as the product of a thickness of the silicon oxide filmformed by performing the sequence SQ11 a single time and the repetitionnumber of the sequence SQ11. The repetition number of the sequence SQ11is set based on a required thickness of the first film SF1.

Referring back to FIG. 17, in the method MTC, the process ST12 is thenperformed. In the process ST12, a second film SF2 is formed on the firstfilm SF1. The second film SF2 is made of silicon oxide. In the processST12, the second film SF2 is formed such that the thickness thereofincreases as a distance of a formation position of the second film SF2from the main surface UL1 increases. By way of example, as shown in FIG.20, a thickness of the second film SF2 formed on the first film SF1 onthe end surface TE2 of the protruded region PJ2 is larger than athickness of the second film SF2 formed on the first film SF1 on the endsurface TE1 of the protruded region PJ1.

For the film forming processing of the process ST12, a process ST12Ashown in FIG. 25A or a process ST12B shown in FIG. 25B may be performed.Hereinafter, the process ST12A and the process ST12B will be described.

The process ST12A includes a process ST121 and a process ST122. In theprocess ST121, plasma of a fifth gas is generated within the chamber 12c. The fifth gas contains silicon atoms and chlorine atoms or hydrogenatoms. The fifth gas may include a SiCl₄ gas or a SiH₄ gas. The fifthgas may be a mixed gas including, by way of example, not limitation, aSiCl₄ gas or SiH₄ gas, an Ar gas and an oxygen gas. In the processST121, the fifth gas is supplied into the chamber 12 c from the gassupply unit 44. Further, the pressure of the chamber 12 c is set to apredetermined pressure by the gas exhaust device 38. Further, the highfrequency powers are respectively supplied to the inner antenna element52A and the outer antenna element 52B from the high frequency powersupply 70A and the high frequency power supply 70B. Further, the highfrequency bias power may be supplied to the lower electrode 18 from thehigh frequency power supply 30. In the process ST121, the fifth gas isexcited into the plasma, and the second film SF2 is formed on the firstfilm SF1 by silicon and oxygen from the plasma. In the subsequentprocess ST122, a purge of the chamber 12 c is performed. The purge ofthe process ST122 is the same as the purge of the process ST11 b.

The process ST12B includes a process ST125, a process ST126, a processST127 and a process ST128. The process ST125, the process ST126, theprocess ST127 and the process ST128 constitute a sequence SQ12. In theprocess ST12B, the sequence SQ12 is performed one or more times.

In the process ST125, a sixth gas is supplied. The sixth gas includessilicon atoms and chlorine atoms. The sixth gas may be a mixed gascontaining, by way of non-limiting example, a SiCl₄ gas and an Ar gas.In the process ST125, the sixth gas is supplied into the chamber 12 cfrom the gas supply unit 44. Further, the pressure of the chamber 12 cis set to a predetermined pressure by the gas exhaust device 38. In theprocess ST125, plasma is not generated. In the process ST125,silicon-containing molecules in the sixth gas adhere to a surface of thefirst film SF1 as a precursor. Then, in the subsequent process ST126,the chamber 12 c is purged. The purge in the process ST126 is the sameas the purge in the process ST11 b. By performing the process ST126,molecules excessively adhering to the first film SF1 can be removed.

In the subsequent process ST127, plasma of a seventh gas is generatedwithin the chamber 12 c. The seventh gas includes a gas containingoxygen atoms. The seventh gas may be a mixed gas containing, by way ofnon-limiting example, an oxygen gas and an Ar gas. In the process ST127,the seventh gas is supplied into the chamber 12 c from the gas supplyunit 44. Further, the pressure of the chamber 12 c is set to apredetermined pressure by the gas exhaust device 38. Further, the highfrequency powers are respectively supplied to the inner antenna element52A and the outer antenna element 52B from the high frequency powersupply 70A and the high frequency power supply 70B. Further, the highfrequency bias power may be supplied to the lower electrode 18 from thehigh frequency power supply 30. In the process ST127, the seventh gas isexcited into the plasma. The layer of the precursor is exposed to activespecies of the oxygen from the plasma. As a result, the layer of theprecursor becomes a silicon oxide film (the second film SF2 or a partthereof). In the subsequent process ST128, a purge of the chamber 12 cis performed. The purge in the process ST128 is the same as the purge inthe process ST11 b.

In a subsequent process ST129, it is determined whether the sequenceSQ12 is to be ended. To elaborate, in the process ST129, it isdetermined whether a repetition number of the sequence SQ12 has reacheda preset number. If it is determined in the process ST129 that therepetition number of the sequence SQ12 has not reach the preset number,the sequence SQ12 is performed again. Meanwhile, if it is determined inthe process ST129 that the repetition number of the sequence SQ12 hasreached the preset number, the process ST12B is ended. A thickness ofthe second film SF2 is defined by the repetition number of the sequenceSQ12. That is, the thickness of the second film SF2 increases as therepetition number of the sequence SQ12 increases. The repetition numberof the sequence SQ12 is set based on a required thickness of the secondfilm SF2.

Referring back to FIG. 17, in the method MTC, a process ST13 is thenperformed. In the process ST13, anisotropic etching is performed on thefirst film SF1 and the second film SF2. Accordingly, the first film SF1and the second film SF2 on one or more protruded regions among theplurality of protruded regions are removed. By way of example, asdepicted in FIG. 21, the first film SF1 and the second film SF2 on theend surface TE1 of the protruded region PJ1 are removed.

In the process ST13, plasma of an eighth gas is generated within thechamber 12 c. The eighth gas may include a fluorocarbon-based gas. Thefluorocarbon-based gas contains fluorocarbon (C_(x)F_(y)) and/orhydrofluorocarbon (C_(x)H_(y)F_(z)). By way of example, thefluorocarbon-based gas may include one or more of CF₄, C₄F₈ and CHF₃. Inthe process ST13, the eighth gas is supplied into the chamber 12 c fromthe gas supply unit 44. Further, the pressure of the chamber 12 c is setto a predetermined pressure by the gas exhaust device 38. In addition,the high frequency powers are respectively supplied to the inner antennaelement 52A and the outer antenna element 52B from the high frequencypower supply 70A and the high frequency power supply 70B. Further, thehigh frequency bias power may be supplied to the lower electrode 18 fromthe high frequency power supply 30. Accordingly, ions are attracted tothe processing target object W from the plasma, and the anisotropicetching of the first film SF1 and the second film SF2 is performed.

A complex film including the first film SF1 and the second film SF2formed at a position having a small distance from the main surface UL1is thin, whereas a complex film including the first film SF1 and thesecond film SF2 formed at a position having a large distance from themain surface UL1 is thick. Accordingly, in the process ST13, it ispossible to remove, among the end surfaces of the plurality of protrudedregions, a part of the end-surface-shaped complex film having the smalldistance from the main surface UL1. For example, as shown in FIG. 21,the first film SF1 and the second film SF2 on the end surface TE1 of theprotruded region PJ1 are removed. The second film SF2 on the end surfaceTE2 of the protruded region PJ2 are left, although the thicknessesthereof is reduced. The remaining first film SF1 and the remainingsecond film SF2 become the second region.

In a subsequent process ST14, the first region, that is, the protrudedregion having the exposed end surface among the plurality of protrudedregions is selectively etched against the second region, that is, thefirst film SF1 and the second film SF2. In the process ST14, thesequence including the above-described processes ST1 and ST2 isperformed one or more times. In the process ST1, among the plurality ofprotruded regions, a part of the protruded region, whose end surface isexposed, including the corresponding end surface is modified. By way ofexample, as shown in FIG. 22, a part of the protruded region PJ1including the end surface TE1 thereof is modified into a modified regionMX. In the subsequent process ST2, the modified region MX is selectivelyremoved, as illustrated in FIG. 23.

The method MTC can be performed in the manufacture of, by way ofexample, a fin type field effect transistor as well as in the etching ofa part of the protruded regions of the processing target object W shownin FIG. 18. In the manufacture of the fin type field effect transistor,a processing target object has a fin region and multiple gate regions.The fin region provides a source region, a drain region and a channelregion. The multiple gate regions are arranged on the fin region.Between neighboring gate regions, the fin region is covered with asilicon nitride film. In the manufacture of the fin type field effecttransistor, there is performed a processing of removing the siliconnitride film and exposing the fin region (the source region and thedrain region) between the neighboring gate regions while protecting themultiple gate regions. This processing is performed to form a contact tothe fin region (the source region and the drain region). The method MTCmay be performed for this processing.

So far, the various exemplary embodiments have been described. However,the exemplary embodiments are not limiting, and various modificationsmay be made. Though the above-described plasma processing apparatus 10is configured as the inductively coupled plasma processing apparatus,various other types of plasma processing apparatuses such as an ECR(Electron Cyclotron Resonator) type plasma processing apparatus, acapacitively coupled plasma processing apparatus, and a plasmaprocessing apparatus using a surface wave such as a microwave ingeneration of plasma may be used in the various exemplary embodimentsand the modifications thereof.

From the foregoing, it will be appreciated that various embodiments ofthe present disclosure have been described herein for purposes ofillustration, and that various modifications may be made withoutdeparting from the scope and spirit of the present disclosure.Accordingly, the various embodiments disclosed herein are not intendedto be limiting. The scope of the inventive concept is defined by thefollowing claims and their equivalents rather than by the detaileddescription of the exemplary embodiments. It shall be understood thatall modifications and embodiments conceived from the meaning and scopeof the claims and their equivalents are included in the scope of theinventive concept.

We claim:
 1. A method of etching a first region made of silicon nitrideselectively against a second region made of silicon oxide, comprising:preparing a processing target object having the first region and thesecond region within a chamber provided in a chamber main body of aplasma processing apparatus; generating plasma of a first gas includinga gas containing hydrogen within the chamber to form a modified regionby modifying a part of the first region with active species of thehydrogen; and generating plasma of a second gas including a gascontaining fluorine within the chamber to remove the modified regionwith active species of the fluorine.
 2. The method of claim 1, whereinthe processing target object is placed, within the chamber, on a stageincluding therein an electrode to which a high frequency power forattracting ions onto the processing target object is allowed to besupplied, and the high frequency power is supplied to the electrode inthe generating of the plasma of the first gas.
 3. The method of claim 1,wherein the processing target object is placed, within the chamber, on astage including therein an electrode to which a high frequency power forattracting ions onto the processing target object is allowed to besupplied, and the high frequency power is not supplied to the electrodein the generating of the plasma of the second gas.
 4. The method ofclaim 1, wherein the second gas includes a NF₃ gas as the gas containingfluorine.
 5. The method of claim 1, wherein the second gas furtherincludes hydrogen, and a ratio of a number of atoms of the hydrogen inthe second gas to a number of atoms of the fluorine in the second gas isequal to or higher than 8/9.
 6. The method of claim 4, wherein thesecond gas further includes a H₂ gas.
 7. The method of claim 6, whereina flow rate ratio of the H₂ gas in the second gas to the NF₃ gas in thesecond gas is equal to or higher than 3/4.
 8. The method of claim 1,wherein the first gas includes a H₂ gas as the gas containing hydrogen.9. The method of claim 1, wherein a plurality of sequences each of whichincludes the generating of the plasma of the first gas and thegenerating of the plasma of the second gas are performed in sequence.10. The method of claim 1, wherein the processing target object furtherhas a third region made of silicon, and the first gas further includes agas containing oxygen.
 11. The method of claim 10, wherein the firstregion is provided to cover the second region and the third region. 12.The method of claim 1, wherein a plurality of sequences each of whichincludes the generating of the plasma of the first gas and thegenerating of the plasma of the second gas are performed in sequence,the processing target object further has a third region made of silicon,the first region is provided to cover the second region and the thirdregion before the plurality of sequences are performed, the plurality ofsequences include one or more first sequences performed until a timeimmediately before the third region is exposed or until the third regionis exposed; and one or more second sequences performed to oxidize asurface of the third region after the one or more first sequences, andthe first gas further includes a gas containing oxygen in at least onesecond sequence.
 13. The method of claim 12, wherein the first gas doesnot contain the gas containing oxygen in the one or more firstsequences.
 14. The method of claim 12, wherein the plurality ofsequences further include one or more third sequences performed afterthe one or more second sequences, and the first gas does not include thegas containing oxygen in the one or more third sequences.
 15. The methodof claim 10, wherein a flow rate ratio of the gas containing oxygen inthe first gas to the gas containing hydrogen in the first gas is set tobe in a range from 3/100 to 9/100.
 16. The method of claim 10, whereinthe gas containing oxygen is an O₂ gas.